1. Field of the Invention
The invention relates to the field of digital television. More exactly, the invention deals with video compression equipments inside television head-ends, which comprise encoders grouped in encoding pools for statistical multiplexing. The invention also concerns of a method for driving individual output bitrates for encoders gathered in such encoding pool.
2. Description of the Prior Art
In the state of the art of television head-ends, it is known, as indicated on the FIG. 1, that a set of encoders MVE, SVEi (where 1<i<N) is organized in pool for sharing a same bandwidth. With this organization in pool one optimizes the picture quality over a constant bandwidth allocated for global output to the set of encoders. So, these encoders MVE, SVEi continuously exchange information to adjust their own video bitrate at a level needed for the best picture quality. Information is transmitted (mainly the video bitrate needs) from slave encoders SVEi in the pool to an encoder MVE assuming bitrate allocation role (master encoder). In a pool, all encoders are identical and each encoder has the ability to be a master. Designation of an encoder as a master is a user decision and this designation can be modified in case of degraded mode of operation. Then, after algorithm calculation, this master encoder MVE redistributes information (individual video bitrate) to each slave encoder SVEi of the pool according to the received request (complexities). This mechanism is statistical multiplexing and is known as “Local Flextream”. Currently this mechanism uses a dedicated RS-485 hardware link (HDLC) with Sub-D 9 pins connectors and specific cable between all the encoders of the pool for the exchange of information.
In FIG. 1, one denotes no particular difference between the streams received by master encoders and slave encoders. Names “UM” or “USi” are only used for naming consistency purpose. A similar remark can be done for streams issued by master encoder “TM” and slave encoders “TSi”.
A disadvantage of this state of the art is this dedicated hardware which is to be set up between all encoders MVE, SVEi: it represents complexity in the design of the encoder pool and associated manufacturing costs.
One of the goals of the present invention is to propose a solution to get rid of this dedicated hardware.
Today, the only known way to use the Flextream capability without the dedicated hardware link is a solution known as “remote Flextream” which consists in deporting the task of allocation outside the head-ends and to assign the new bitrate allocation through an external network (Wide Area Network). But the remote Flextream carries some drawbacks: it is expensive to deploy for small head-ends since it requires the use of additional equipments (multiplexers) and it is less accurate than the local Flextream. Finally, it generates a waste of bandwidth and consequently a worse picture quality.
Another advantage of the invention is that it can dispense with the use of a proprietary multiplexer compatible with “remote flextream” mode and then to benefit a larger flexibility in designing systems by using multiplexer “on the shelf” and/or low-cost which do not perform this “remote flextream” mode.